The invention relates to a cap for a tube for extracting blood or the like, with a base, a cannula cone placed on the base and a skirt connected to the base having a locking mechanism for fixing the cap to the cylindrical body of the tube.
It is already known to provide injection syringes with a removable cap, to make it possible to better clean a syringe, which is intended for use more than once. Moreover, a removable cap makes it possible to adapt cannulas of different diameters to the same injection syringe cylinder. The attachment and locking of the cap to the injection syringe cylinder is normally effected with a thread, where the cap skirt is provided with an internal thread and the lower end of the syringe cylinder with an external thread. However, it is also possible to use bayonet catches and spring catches as a locking element.
If such an injection syringe is used for extracting blood, the doctor or nurse sticks the cannula with the plunger or piston rod initially completely depressed in the direction of the cap into the vein of a patient and then raises the piston rod connected to the syringe piston. As a result of this raising or pulling up action, the blood is sucked into the syringe cylinder. This requires two hands, because the syringe inserted in the vein must be held with one hand, whilst the other hand is used for raising the piston.